Method of preparing ammonium nitrate explosives



Patented Nov. 12, 1940 UNITED STATES PATENT OFFICE f METHOD OF PREPARINGAMIVIONIUM NITRATE EXPLOSIVES No Drawing.

Application August 9, 1939,

Serial No. 289,188

8 Claims.

This invention relates to a new and improved method of preparingammonium nitrate explosive compositions and more especially to thepreparation of explosives possessing superior sensitiveness properties,particularly at high densities.

In the case of existing ammonium nitrate high explosives sensitized bymeans of non-explosive solid sens-itizers, very careful control andhandling are necessary in order that the product shall maintain itsexplosive properties unimpaired during storage. The aflinity of ammoniumnitrate for water makes this particularly important, since ammoniumnitrate has a tendency to become hard and insensitive in the presence ofeven small amounts of water.

The object of the present invention is a novel method of preparingexplosives of high ammonium nitrate content. A further object is amethod of preparing such explosives whereby so they possess improvedsensitiveness characteristics, particularly at high densities.Additional objects will be disclosed as the invention is furtherdescribed hereinafter. l The foregoing objects are accomplished by themethod of our invention whereby ammonium nitrate and a sensitizertherefor are heated with an additional inorganic salt capable ofreacting with ammonia and are maintained exposed to the action ofammonia gas during at least a portion of the heating. vWhile the aboveprocedure is our preferred one, in some cases heating of the mixture isunnecessary.

Various methods are available for carrying out our invention. Onedesirable procedure comprises including a metal cyanamide as aningredient of the ammonium nitrate composition. Calcium cyanamide, forexample, on heating to 80-85 0., reacts as follows with ammoniumnitrate:

The same effect wouldbe obtained when other metal cyanamides than thatof calcium were used,

If the heat- (Cl. 52r19) for example the cyanamides of barium,strontium,

zinc, and copper.

While the use of a metal cyanamide, and particularly calcium cyanamide,is a convenient and preferred embodiment of-our invention, the desiredresults may be obtained by other means. We may, for example, include inthe ammonium nitrate composition an inorganic salt capable of forming anammoniate with ammonia, or of reacting otherwise, and then introducegaseous ammonia, whether formed externally or as a product of a reactiontaking place within the mixture. Salts which are effective for thepurpose include calcium nitrate, barium nitrate, strontium nitrate, zincnitrate, lead nitrate, cobalt nitrate, copper nitrate, cobaltperchlorate, and the like.

In carrying out our invention we find its greatest advantage to lie inits application to ammonium nitrate compositions of a relatively loworder of sensitiveness. method, greatly increased sensitiveness isobtained. It is particularly applicable in high density ammonium nitratecompositions, and by its use densities may be employed satisfactorilysives without impairment of propagation properties.

A suitable composition of explosive for use according to our inventionmay include a preponder- By the employment of ourant amount of ammoniumnitrate, 'anorganic will serve as specific embodiments.

Example 1 Ammonium nitrate in the amount of 17.6 lbs. j

was introduced into a mixing vesselhavingaxtight cover and adapted to beclosed tightlyand was j heated to 80 C. 2.4 lbs. of dinitrotoluene wasthen added and the mix was maintained at a tem perature of 80 C. for 15minutes. allowed to cool to 35 C. The materialwas packed intowater-tight metal containers. of 2-inch di-' ameter at a density of1.20. Powder thus packed was tested for propagation when primed with aIt was then the prior art at a density around'1. 20.

Example 2 Ammonium nitrate in the amount of 17.0 lbs. was introducedinto the mixing vessel of Example 1 and heated to C. A mixture of 2.4lbs. of dinitrotoluene and 0.6 lb. of calcium cyanamide was added to theheated ammonium nitrate, and the mixer closed. The whole was maintainedat 80 C. for 15 minutes, after which it was allowed to cool to 35 C. Thepowder was packed in metal containers of 2" diameter at a density of1.37. When tested at this density, the explosive propagated at avelocity of 3495 meters per second. This example illustrates theincreased sensitiveness and propagating power, at high packingdensities,- of explosive compositions according to our invention.

Example 3 A blend of 17.3 lbs. of ammonium nitrate and 0.3 lb. ofparaflin was introduced into a mixing vessel adapted to be closedtightly, and was heated to 80 C. A mixture of 1.8 lbs. of dinitrotolueneand 0.6 lb. of calcium cyanamide was then added to the heated blend andthe-whole was maintained at 80 C. for 15 minutes. The blend was allowedto cool to 35 C. and was packed to various densities in metal containersof 2" diameter. The material was insensitive to the action of a No. 8blasting cap at a density of 1.0, but at as high a density as 1.35detonated with a velocity of 3400 meters per second when primed with abooster charge similar to that used in Example 1. At a density of 1.30,the material propagated across an air gap of 4 inches.

Example 4 Ammonium nitrate in the amount of 12.8 lbs. was introducedinto a mixing vessel such as used in Example 1, and was heated to atemperature of 80 C. A blend of 1.5 lbs. of trinitrotoluene, 0.45 lb. ofcalcium cyanamide, 0.225 lb. of brewers grits, and 0.03 lb. of a coatingmaterial was then added to the heated ammonium nitrate, and the entiremixture was maintained at. 80 C. for 15 minutes with continuousagitation. The blend was allowed to cool to 25 C., and was then packedinto 1% x 8" cartridges of a density such that the average weight percartridge was 168 grams. Under such conditions, the cartridges weresensitive to, and capable of initiation by, a commercial blasting cap,showing a velocity of 4100 meters per second. The sensitiveness by thewhole-stick propagation test was 10 inches. and the explosive showed acomparatively good de ree of water resistance.

Example 5 A mixture was made, in a mixing vessel capable of being closedtightly, of 16.3 lbs. of ammonium nitrate, 2.4 lbs. of dinitrotoluene,and 1.0 lb. of hydrated cupric nitrate. Suflicient gaseous ammonia wasintroduced to constitute slightly more than 0.3 lb. The container wasmaintained tightly closed for a short period of time, and the powder wasthen packed to a density of 1.30 in metal containers of 2" diameter. Atthis density the explosive gave consistent high velocity detonationswhen suitably primed. It was demonstrated that the reaction product ofammonia with the cupric nitrate had efiected a sensitization of theexplosive, since a similar composition, withthe only difierence that noammonia was introduced, failed to detonate consistently at densitiesabove 1.20.

Example 6 Ammonium nitrate in the amount of 16.6 lbs. was blended with1.8 lbs. dinitrotoluene, 0.3 lb. parafiin, and 1.0 lb. calcium nitratein a mixing vessel capable of being closed tightly. Sufl'icient gaseousammonia was introduced to comprise slightly more than 0.3 lb. and thecontainer was closed. After being maintained for a period of time in thepresence of ammonia gas, the powder was packed into metal containers of2" diameter. At a density of 1.3, the velocity of detonation wasdetermined at 3200 meters per second. This example illustrates anembodiment of the invention in which the ingredients were mixed cold.

In the foregoing examples the sensitizers have been nitro-aromaticcompounds, and specifically nitrotoluenes. It should-be understood,however, that various organic sensitizers are available and applicableother than nitrotoluenes, for example, the various nitronaphthalenes,diphenylamirle, diphenyl, and the like. The organic sensitizer ispreferably one having a melting point such that the material is at leastpartially fused at the temperature of mixing of the explosive; hence itshould desirably have a fusion point below C. In carrying out our methodlikewise, where the ingredients are heated together under confinement,it will be desirable to maintain the temperature below 100 C. It will beunderstood also that inorganic sensitizers may be used,

for example, aluminum, ferrosilicon, calcium silicide, sulfur, and thelike.

The compositions according to our invention will contain more than 50%ammonium nitrate and preferably more than 75%. The organic sensitizerwill desirably be present in an amount between 0.5 and 20%, while theproduct of the reaction between the inorganic salt and ammonia should bepresent in an amount between 0.1 and 10%. Specific favorablecompositions are shown in the examples cited previously.

The advantages of our invention are very considerable. By way ofillustration, certain types of ammonium nitrate explosives are disclosedin the art which are sensitized by means of nonexplosive sensitizers.Compositions of this type are generally relatively insensitive. Certainof them are so much so that they are incapable of detonation by means ofa commercial blasting cap but can be detonated when initiated by asuitable amount of a booster charge of trinitrotoluene, and then explode.with undiminished high velocity. Explosives of this type areparticularly efiective in quarry blasting, and it is frequentlydesirable to obtain as high a loading density as possible in theborehole in order to secure the maximum blasting execution. Withexplosives of such a relatively low order of sensitiveness, however,densities greater than 1.15 are generally undesirable in the case ofcompositions of the prior art, since there is too great a chance offailure to detonate. Operating in accordance with the present invention,however, densities up to 1.7 are practically utilizable. Preferably theexplosive will be enclosed in a completely water-tight container, suchas a metal can. Not only is the invention applicable to capinsensitiveexplosives, but it is effective also in the case of cap-sensitiveexplosives which are thereby made more certainly detonable. It maylikewise be utilized to sensitize cap-insensitive compositions and makethem sensitive to commercial blasting caps. Furthermore, it isapplicable in the case of certain explosives of high ammonium nitratecontent, which thereby become practical for use in smaller diametersthan would otherwise be possible.

The method of our invention is applicable to the preparation of theexplosive compositions disclosed in our copending applicaton, Serial No.289,187, dated August 9, 1939.

We have described our invention at length in the foregoing, but it willbe understood that many variations in procedures and compositions may beintroduced without departure from the spirit of the invention. We wishto be limited, therefore, only by the following patent claims.

We claim:

1. The method of preparing explosive compopositions of high ammoniumnitrate content, which method comprises mixing togetherammoniumvnitrate, an organic sensitizer therefor, an inorganic nitrateother than those of the alkali metals and capable of reacting withammonia, and ammonia, and maintaining said mixture in the presence ofgaseous ammonia.

2. The method of preparing explosive compositions of high ammoniumnitrate content, which method comprises heating together ammoniumnitrate, an organic sensitizer therefor, and an inorganic nitrate otherthan those of the alkali metals and capable of reacting with ammonia,maintaining said mixture exposed to the action of ammonia gas duringsaid heating, and cooling said mixture while still in the presence ofgaseous ammonia.

3. The method of claim 2, in which the inorganic nitrate is calciumnitrate.

4. The method of preparing ammonium nitrate explosive compositions,which method comammonium nitrate, an organic sensitizer therefor, and ametal cyanamide, heating said mixture and maintaining the same exposedto the action of ammonia gas during said heating, and cooling saidmixture while still in the presence of gaseous ammonia.

7. The method of preparing ammonium nitrate explosive compositions,which method comprises mixing together a preponderant amount of ammoniumnitrate, an organic sensitizer therefor, and calcium cyanamide, heatingsaid mixture, and maintaining the same exposed to the action of ammoniumgas during said heating, and cooling said mixture while still in thepresence of gaseous ammonia.

8. The method of preparing explosive compositions of high ammoniumnitrate content, which method comprises mixing together ammoniumnitrate, an organic sensitizer therefor, an inorganic nitrate other thanthose of the alkali metals and capable of reacting with ammonia, and

heating said mixture in a closed system.

MELVIN ALONZO COOK. CLYDE OLIVER DAVIS. WALTER EASTBY LAWSON.

